Reflection and Refraction


          Reflection is the change in direction (position) of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

         Refraction is the change in direction (position) of a wave due to a change in its speed. This is most generally observed when a wave passes from one medium to another medium at an angle.


 Reflection of light is either diffuse (retaining the energy, but losing the image) or specular (mirror-like) depending on the nature of the interface. Furthermore, if the interface is between a conductor and a dielectric, the phase of the reflected wave is retained; otherwise if the interface is between two dielectrics, the phase may be inverted or retained, depending on the indices of refraction.

Types of reflection:

  • Diffuse reflection
  • Retroreflection
  • Complex conjugate reflection
  • Neutron reflection
  • Sound reflection
  • Seismic reflection

Laws of reflection:

The laws of reflection are as follows:

  1. The incident and the reflected ray and then normal to the reflection surface at the point of the incidence lie in the same plane.
  2. The angle which the incident ray (i) makes with the normal is equal to the given angle which the reflected ray makes to the same normal.
  3. Light paths are reversible.


Refraction of light is the most generally observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.

Refraction is described by Using Snell’s law, which states that the angle of incidence θ1 is related to the angle of refraction θ2 by

 Sin θ1/sinθ2 = v1/v= n2/n1

Here v1 and v2 are the wave velocities in the respective media, and n1 and n2 the refractive indices.

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